Structure of a subject along an image-capturing direction, that is, information along a depth direction, cannot be acquired only by one projected image obtained by a transmission electron microscope and the like. In this case, information along the depth direction of the subject can be acquired by spreading gray scale intensities of a plurality of projected images captured from a plurality of angles within the image-captured angles, integrating them together, and examining the integration thereof.
However, by a simple integration of gray-scale intensities of a plurality of projected images, which was captured from a plurality of angles and spread within the image-captured angles, integrations of the gray-scale intensities may arise at the positions where the subject originally did not exist, to give false information, which shows as if the subject existed there. Conventionally, it was difficult to suppress or remove the above-described false information. Accordingly, it was impossible to acquire 3-dimensional image data that correctly express the structural configuration of the subject by processing the projected image data obtained by projecting the subject toward the plural angles.